Multi-mode mobile communication devices are popular in certain regions of the world for a variety of reasons. For example, since new communication systems are initially deployed in limited areas, it may be desirable for a mobile communication device to be able to communicate using a mature, widely-deployed system in addition to a newer system. One example of a next generation communication system is that specified by the Institute of Electrical and Electronic Engineers (IEEE) specification 802.16, known by the trade name WiMAX. A more conventional system would be, for example, that specified by the Global Specification for Mobile communication (GSM) specification. WiMAX provides greater data throughput compared to GSM and its associated data air interface, but is still in the development stage. WiMAX systems will be deployed in areas also served by GSM systems. However, as WiMAX service will not initially be as widely available is GSM service, some subscribers may wish to have access to both systems without having to carry separate mobile communication devices for each system. A multi-mode communication device can be designed with a single modem, and switch from one air interface to another, but it may be more preferable to have dedicated modems in the multi-mode communication device, each for a different air interface, and each being allowed to operate simultaneously. However, having multiple modems in a multi-mode communication device requires more volume, and it draws more power.
Market pressures have compelled manufacturers to constantly reduce the volume of mobile communication devices, or at least reduce the volume of components so that additional sub-systems can be included. A significant volume of a mobile communication device is taken up by the battery. As a result, battery size has been reduced over generations of mobile communication devices. While the electrical efficiently of mobile communication devices has increased substantially, a factor which has facilitated the use of smaller batteries, battery technology has not kept pace. As a consequence, operating multiple modems in a multi-mode mobile communication device using a present conventional-sized battery can result in peak current being drawn from the battery which results in significant battery voltage droop due to the internal resistance of the battery.
High current conditions exist when, for example, both modems are active and transmitting, such as during the handover process when handing a call over from one modem to another modem in the communication device. This is due to both modems having to transmit on their respective air interfaces at overlapping time periods—one modem continues with the call as well as signaling to the respective communication system to commence with the handover while the other modem must likewise signal to its corresponding communication system to receive the call from the first communication system. Without any control, peak current while both modems are transmitting can cause voltage drop out or droop to a level below a minimum operating voltage, possibly resulting in the communication device resetting.
Accordingly, there is a need to control the power consumption of a multi-mode mobile communication device.